We review the main information that we have obtained from combined Raman spectroscopy and electron diffraction experiments on individual free-standing single-walled carbon nanotubes. This information concerns: the radial breathing mode vs diameter relationship; the dependence of the frequency and lineshape of the G-modes in semiconducting and metallic tubes; the evaluation of the optical transition energies for individual free-standing SWNTs. From these data, we can define Raman criteria allowing the indexing of carbon nanotubes from their Raman features only. We show the efficiency of this approach to assign the (n,m) indices of individual chiral and achiral single-walled carbon nanotubes. These criteria are also applied to identify tubes grown on a substrate from a single wavelength Raman experiments. These results obtained on index-identified individual nanotubes are compared with theoretical predictions

The temperature dependence of the Raman spectrum of a gelatine-based composite material doped with single-walled carbon nanotubes (SWNT@gelatin) is reported. A significant up-shift of the G-mode frequency is observed when the temperature is decreased from room temperature to 20~K. This frequency shift is significantly stronger than the one found for pure thermal effects. In contrast, the features of the radial breathing modes (frequencies and width) display no significant change in the same temperature range. These results are well understood by considering a uniaxial strain on the nanotube induced by the thermal expansitivity mismatch between the nanotube and the surrounding matrix.

We have investigated and evaluated different TEM sample preparation techniques for studying carbon single-walled nanotube (C-SWNT) nucleation and growth, issued from CVD processes when the catalyst is supported on a substrate. This kind of study requires means to observe individual and isolated tubes. It implies using synthesis conditions able to produce only a low density of tubes and to thin the substrate to electron transparency, to observe the nanotubes and the catalytic particles from which they have grown in their native state. We have tested two approaches, depending if the substrate is thinned after or before the synthesis. The low tube density requirement led us to exclude all the techniques where the substrate is thinned to electron transparency after the synthesis. We have shown, that, with this last approach, all TEM preparation techniques dramatically suffer from a lack of control of thin areas with respect to the location of the tubes, which is unknown. However we have demonstrated that the suitable approach is to perform synthesis directly on transparent substrates presenting several holes. We have tested the capabilities and the potentialities of these supports for studying the size distribution and composition of the catalytic particles, the nucleation mode, the diameter and helicity of the tubes. These results are very promising and represent an important step for performing specific nanoscale TEM analyses necessary for the study of the growth mechanism of nanotubes on substrates. (C) 2009 Elsevier B.V. All rights reserved.

From combined Raman spectroscopy and electron diffraction studies on several freestanding single-walled carbon nanotubes (SWNTs), we define Raman criteria which correlate the main features of the Raman spectrum (radial breathing mode and G modes) and the optical transition energies with the structure of the SWNT under investigation. On this basis, we discuss the possibilities to determine the (n,m) indices of an individual SWNT from a single wavelength Raman experiment. We show the efficiency of this approach in assigning the (n,m) structure of different individual nanotubes including all types of achiral SWNTs. Finally, the limits and the accuracy of the method are discussed.

The Raman spectral signature of folded graphene layers for one to six layers was studied. Folding allows realization of rotational disorder in otherwise perfect samples. We show that the two-dimensional Raman band of the folded sample is up shifted compared to the unfolded sample. The evolution of the spectral signature with increasing number of layers is discussed.

In their Comment, Ni et al. show new data as supporting their hypothesis, i. e., the two-dimensional band blueshift between graphene and misoriented bilayer is caused by a reduction in the Fermi velocity. In the first part of our reply, we will demonstrate that the exhibited data, which typically shows a constant blueshift for various excitation energies are in contradiction with a change in Fermi velocity. In the second part we will explain how charge transfer from the substrate that affects the phonon-dispersion curve can account for the observed discrepancies and how this hypothesis is supported by experimental observations.